1. Field of the Invention
The present invention relates to a GaP red light emitting diode (LED) having a high luminance level.
2. Description of the Prior Art
Heretofore, GaP red LEDs have generally been fabricated by the liquid-phase epitaxial growth method. In this epitaxial growth method, an n-type GaP epitaxial layer doped with Te is grown on an n-type GaP substrate. Subsequently, from a Ga melt added with Zn and Ga.sub.2 O.sub.3, a p-type GaP epitaxial layer is grown and deposited on the n-type GaP epitaxial layer, thus making a p-n junction. The resulting crystal is annealed at about 500.degree. C. with the result that Zn-O pairs are created. The Zn-O pairs form an emission center from which red light is emitted.
The GaP LEDs of the type described often cause a problem of luminance reduction or drop and, hence, a satisfactory solution of this problem has been desired. However, there have been considerable difficulties in clearing up factors having direct connection with the luminance reduction.
Through a lengthy and careful investigation on the cause of the luminance reduction of the GaP red LEDs, the present inventors uncovered the fact that the luminance reduction is closely related to the impurity concentration of the n-type epitaxial layer, more particularly to the Si concentration and S concentration. Based on this finding, the present invention was made.